1. Field of the Invention
This invention relates to a resin molded semiconductor device and its manufacturing method.
2. Description of the Related Art
To manufacture a resin molded semiconductor device, a lead frame is prepared, each of various kinds of semiconductor dice, a passive element or the like is die-bonded to the lead frame with solder, silver paste or the like, the semiconductor die or the like and the lead frame are electrically connected by wire-bonding or the like through an aluminum wire or a gold wire, and then the semiconductor device is completed by resin-molding the lead frame excluding outer lead portions, followed by cutting a tie bar and folding the leads or the like as required.
The assembly process of the resin molded semiconductor device as mentioned above is described, for example in “All about Leading Edge Packaging Technologies—with Illustrations” edited by Handotai Shingijutsu Kenkyukai, Sep. 25, 2007, published by Kogyo Chosakai Publishing Co., Ltd.
In the assembly process of the resin molded semiconductor device as described above, an unnecessary resin film 104 is inevitably formed in a region surrounded by a resin package 101 that is filled with the resin, outer leads 102 and a tie bar 103 as shown in FIG. 4 at a completion of a resin-molding process step, as a result of the resin molding method. However, a resin leakage portion 105 as shown in FIG. 4 is usually not formed on a surface of the tie bar 103 or the outer lead 102. It is because resin injection in the resin-molding is carried out while an upper mold 115 and a lower mold 106 apply a high pressure to a lead frame 107 which bears a semiconductor die 108 bonded thereon and electrically connected with the semiconductor die 108 through a bonding wire 110 or the like as shown in FIG. 5 so that the resin does not leak.
In this case, the tie bar 103, which is formed between the outer leads 102 and serves to hold the outer leads 102 until the resin-molding process step is completed, also serves as a dam bar 109 as shown in FIG. 5 and FIG. 6 to block and prevent the injected resin from leaking out of the resin package 101. Therefore, the injected resin neither leaks out of the dam bar 109 nor forms the resin leakage portion 105 on the surface of the tie bar 103 or the outer lead 102 outside the resin package 101, although the injected resin forms the unnecessary resin film 104 in the region surrounded by the resin package 101, the outer leads 102 and the dam bar 109, i.e. the tie bar 103.
However, what is stated above holds true only when the surfaces of the lead frame 107 have flatness and are firmly and tightly pressed against the upper mold 115 and the lower mold 106 in the resin-molding process step. In reality, however, the lead frame 107 that is formed by punching has burrs 111 consisting of fine projections and depressions on its surface as shown in FIG. 7B that is an enlarged view of a portion marked with a dashed line circle in FIG. 7A. Thus there are caused very narrow gaps between the lead frame and the mold in some cases, even when the lead frame 107 is pressed by the upper mold 115 and the lower mold 106 from above and below. As a result, the resin leaks through the gaps to form the resin leakage portion 105 made of thin resin film on the surfaces of the tie bar 103 and the outer leads 102 as shown in FIG. 4. The resin leakage portion 105 flakes off in a subsequent process step such as folding the leads to make dust that causes problems in yield and reliability.
It should be noted that the resin film 104 formed in the region surrounded by the resin package 101, the outer leads 102 and the tie bar 103 can be relatively easily removed by sandblasting, air showering or the like and that the resin leakage portion 105 sticking firmly to the outer leads 102 and the like can be not easily removed by the means mentioned above.